Patricia and Derek couldn't have chosen a worse time to begin trying to conceive. Derek's sister had just died, completely unexpectedly. Still, it was that event that pushed them to make up their minds in the first place.

Though stressful, "it was a crystallizing moment for both of us," Patricia recalls.

But after nine months of trying, the couple sought out a fertility specialist and began a regimen of treatment that millions of women are currently undergoing, many in its most high-tech form, in vitro fertilization (IVF).

"Each month was another cycle of stress and depression," Patricia recalls. "Do the meds, do the drugs, do the blood tests, have the ultrasound, have sex, wait for test results, do the meds, do the drugs... Then you get your period, and it is like a death. But you only have a few hours to grieve before you have to start the pills and the needles and the tests again."

After three months, Patricia was both literally and figuratively sick and tired of the process—and more stressed than ever. When their physician suggested the couple take a break before considering the next step, Derek and Patricia knew it was the right thing to do.

"After two months of being off any treatments, I was still feeling sick: weak, fatigued, nauseated," Patricia says. "I was pretty frustrated, so I called my doctor to ask when we might resume treatment. She asked when my last period was, and I told her I still hadn't gotten a period since our last failed treatment in early June."

Andy—Patricia and Derek's son, conceived during their very first "off-treatment" cycle—was born in April of 1997.

Patricia and Derek's story is the kind that will likely make anyone wince who has wrestled with fertility issues. If you've tried to become pregnant and had even the slightest hint of trouble, you've probably been told one or two—or a dozen—similar tales, most of which end with the cliched assertion that if you want to get pregnant all you have to do is stop trying so hard and relax. It's enough to make you want to strangle someone.

According to the American Society for Reproductive Medicine, well over 6 million Americans—about 10 percent of those of reproductive age—struggle with infertility, which is defined as not being able to achieve a pregnancy after trying for 12 months (six, if you're a woman 35 or over). Those aren't the most encouraging numbers, but what is perhaps most disturbing about them is that you rarely know ahead of time whether they do or don't, will or won't, apply to you.

For many couples who have decided to try to begin or expand their family, that means each month's hastily unwrapped negative pregnancy test brings with it a little more stress, a little more disappointment, a little more guilt—and maybe a lot more depression. But a growing body of evidence suggests that those feelings may tip the mind-body balance so that the next test is negative again. The question is, just how vicious is this particular cycle?

As Patricia discovered, a low mood is linked to low fertility. "Research shows that a woman who has a history of depression is twice as likely to subsequently experience infertility as a woman with no history of depression," says Alice Domar, of The Domar Center for Complementary Healthcare, in Waltham, Massachusetts.

It's no better at the other end of the street. Domar cites surveys showing that women who are infertile are as stressed-out as those who suffer from cancer, AIDS or heart disease.

Widely considered the preeminent expert on the relationship between mood and fertility, Domar has herself conducted studies showing that the more stressed a woman is, the less likely she is to achieve pregnancy with the higher-tech infertility treatments, like IVF. Even more compelling, she's demonstrated that when women are taught a meditative practice known as the "relaxation response" along with visualization, yoga and participate in support groups, the likelihood of pregnancy rises sharply.

Others have highlighted a link between the stress of infertility treatment and the outcome of that treatment. Depression, for example, is associated with high rates of dropout from infertility treatment.

In fact, emotional stress is the second-most frequently cited reason for dropping out of infertility treatment, trailing only financial constraints. It's not that the treatments are difficult, but that the people undergoing them simply can't take the conception-related pressure for long. In one Swedish study, a group of couples having trouble conceiving was offered three free cycles of IVF. Fifty-four percent dropped out of the program before completing all three cycles. The reason most commonly given was psychological stress. In an Australian study, couples offered six free IVF cycles completed only 3.1, on average; again, stress and mood effects were the top reasons cited for dropping out.

When treatment and its attendant stresses stop, pregnancy occurs often enough to be a documented phenomenon. A 2004 study from the Netherlands found that 26 percent of women who chose to drop out of fertility treatment after their first cycle went on to become pregnant without further treatment. Thirteen percent of women who dropped out after the second treatment cycle also became pregnant afterward.

Exactly how perceived stress results in reduced fertility is still sketchy, but the links in the chain of causation are becoming clearer. Negative emotions can kick stress hormones like cortisol into overdrive. Those stress hormones, in turn, alter physiology in ways that can be at odds with conception—by lengthening the menstrual cycle, for instance.

While women shoulder most of the burden of fertility-related stress, it is not theirs exclusively. Men experiencing psychological distress tend to produce fewer sperm and ejaculate sperm with lower motility. In a study of more than 800 couples followed over 12 months, researchers from the United Kingdom and Denmark showed that stress in men—in particular, personal and marital stresses—led to a lower likelihood of achieving pregnancy via infertility treatment.

Still, the impact of male stress on fertility is much weaker than is the impact of female stress. The external pressures placed on men to reproduce are significantly less than those placed on women, and their response to those stresses is correspondingly less intense.

An evolutionary perspective provides added logic. Stress creates an inhospitable environment for sustaining a pregnancy. Stress hormones signal the presence of some kind of external crisis—and a crisis does not supply the most advantageous conditions for sustaining a pregnancy for nine months. A body that is receiving a constant barrage of distress signals does not put its main focus on pouring time and energy into conception.

Men, as the Danish researchers pointed out, "contribute to conception but not to actual pregnancy, limiting the time interval in which their emotions can influence the biological event relative to women." While a woman's mood can influence everything from fertilization to implantation to fetal growth, a man's mood plays a role only in the production and delivery of sperm.

Just how important mood is in men and women is itself unclear: a fact that will frustrate some and buoy others.

A study in the journal Human Reproduction disputed Domar's findings that stress diminishes the effectiveness of IVF. It followed 166 women from before they began IVF to right before egg retrieval. The researchers searched for some factor that could discriminate between those who later conceived during that particular cycle and those who didn't. They found none.

Teasing out a link between mood and fertility is even more difficult when researchers look not at people undergoing high-tech infertility treatments but at the mass of humanity simply setting out to try to conceive a child the old-fashioned way.

"Do I think that mood plays a critical role in conceiving?" asks Kris Bevilacqua, a psychologist at New York's Montefiore Institute for Reproductive Medicine and Health. "Yes and no. No, because women who are raped conceive. And yes, because when couples are in a good mood, feeling positive and optimistic, it helps them go further, try a little harder."

Where does that leave you? Domar's studies suggest that mood influences the success of infertility treatment. But no data show that the treatment of psychological distress leads to any rise in pregnancy rates among the general population.

And as for all those people who tell you "just relax, you'll get pregnant in no time," they don't really have a clue what they're talking about, notes William Petok, chairman of the mental health group of the American Society of Reproductive Medicine. "Besides, I've never met anybody to whom you could say, 'Just relax,' and they'd do it. So it's bad advice."

And to whom does it even apply? "Most couples do not begin their reproductive efforts with feelings of depression and anxiety," observes Madeline Licker Feingold, director of psychological services at Alta Bates In Vitro Fertilization Program in Berkeley, California. "In fact, most people take fertility for granted—usually having spent many years guarding against an unplanned pregnancy—and begin the process of family building with hope, joy and excitement. Then they are shocked to learn of their infertility and often torment themselves for wasting time with birth control and waiting too long to try to conceive."

If you have a history of depression or anxiety, it would be wise to talk to a doctor, Domar advises. "I recommend that anyone who wants to get pregnant get their distress level under control before even trying to conceive ."